1. Field of the Invention
The present invention relates to dielectric ceramic compositions used such as dielectric layer of multilayer ceramic capacitor and electronic devices used as dielectric layer of the dielectric ceramic compositions.
2. Description of the Related Art
Multilayer ceramic capacitor is broadly used as small size, large capacity and highly reliable electronic device and that a large number of the multilayer ceramic capacitors is used in electric equipments and electronic equipments. Recently, as equipments get smaller in size and higher in performance, demands for smaller size, larger capacity, lower cost and higher reliability for the multilayer ceramic capacitor are becoming more strict.
Multilayer ceramic capacitors are normally manufactured by laminating the internal electrode layer paste and dielectric slurry (paste) by sheet method or printing method and firing them. For the internal electrode past, normally Pd or Pd alloys have been used, however, instead of the costly Pd, relatively low priced Ni or Ni alloys are being used.
Now when forming internal electrodes by Ni or Ni alloys, firing in an atmosphere leads to the oxidation of the electrodes. Therefore, generally, after debinder, it is required to fire in reducing or neutral atmosphere.
But multilayer ceramic capacitor having the internal electrode made of Ni or Ni alloys, in comparison to the internal electrode made of Pd manufactured by firing in an atmosphere, had problems of being shorter life for insulation resistance and being unreliable.
The dielectric ceramic compositions of multilayer ceramic capacitors disclosed in The Patent Article 1; Japanese Unexamined Patent Publication 3-133116 and The Patent Article 2; Japanese Patent Publication 2787746 are known to lengthen the insulation resistance life at the dielectric ceramic composition of multilayer ceramic capacitor having internal electrode made of Ni or Ni alloys.
According to The Patent Article 1, by using dielectric ceramic composition containing dielectric oxide having a certain composition and including a predetermined amount of one or more kinds selected from compounds that are oxides of Y, Gd, Th, Dy, Zr, V, Mo, Zn, Cd, Tl, Sn, and P and/or the oxides of those by firing, the insulation resistance life can be lengthened.
According to The Patent Article 2, by using dielectric ceramic composition containing dielectric oxide having a certain composition and including a compound which a certain amount of Mn oxides and/or the Mn oxides by firing, and a compound which a certain amount of Y oxides and/or the Y oxides by firing, the insulation resistance life can be further lengthened.
Further, according to the dielectric ceramic compositions as in the Patent Articles 1 and 2, main composition {{Ba(1-x-y) CaxSry}O}A{Ti(1-z)Zrz}BO2 may be added with Mg oxides as subcomponent. However, these articles do not disclose the composition amount rate of Mg and Ca to lower the initial insulation resistance percent defective, namely the IR defect rate. Further, dielectric ceramic composition as in Patent Article 1 has a problem that since it includes much Ca, relative dielectric constant becomes lower.